Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for touch sensing, and more specifically, a capacitive touch sensing device having an array of sensor electrodes with underlying routing traces for improved transcapacitive sensing, and methods for using the same.
Description of the Related Art
Input devices including proximity sensor devices (also commonly called touchpads or touch sensor devices) are widely used in a variety of electronic systems. A touch sensor device typically includes a sensing region, often demarked by a surface, in which the touch sensor device determines the presence, location and/or motion of one or more input objects. Touch sensor devices may be used to provide interfaces for the electronic system. For example, touch sensor devices are often used as input devices for larger computing systems (such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers). Touch sensor devices are also often used in smaller computing systems (such as touch screens integrated in cellular phones).
Many touch sensor devices utilize an array of sensor electrodes to measure a change in capacitance indicative of the presence of an input object, such as a finger or stylus, proximate the sensor electrodes. Some capacitive implementations utilize “self capacitance” (or “absolute capacitance”) sensing methods based on changes in the capacitive coupling between sensor electrodes and an input object. In various embodiments, an input object near the sensor electrodes alters the electric field near the sensor electrodes, thus changing the measured capacitive coupling. In one implementation, an absolute capacitance sensing method operates by modulating sensor electrodes with respect to a reference voltage (e.g. system ground), and by detecting the capacitive coupling between the sensor electrodes and input objects. Absolute capacitance sensing methods are very effective in detecting the presence of a single input object, even when spaced far from the surface of the touch sensor device.
Other capacitive implementations utilize “mutual capacitance” (or “transcapacitance”) sensing methods based on changes in the capacitive coupling between sensor electrodes. In various embodiments, an input object near the sensor electrodes alters the electric field between the sensor electrodes, thus changing the measured capacitive coupling. In one implementation, a transcapacitive sensing method operates by detecting the capacitive coupling between one or more transmitter sensor electrodes (also “transmitter electrodes”) and one or more receiver sensor electrodes (also “receiver electrodes”). Transmitter sensor electrodes may be modulated relative to a reference voltage (e.g., system ground) to transmit transmitter signals. Receiver sensor electrodes may be held substantially constant relative to the reference voltage to facilitate receipt of a resulting signal. A resulting signal may comprise effect(s) corresponding to one or more transmitter signals, and/or to one or more sources of environmental interference (e.g. other electromagnetic signals). Sensor electrodes may be dedicated transmitter electrodes or receiver electrodes, or may be configured to both transmit transmitter signals and receive resulting signals. Transcapacitive sensing methods are very effective in detecting the presence of a multiple input objects in a sensing region and input objects that are in motion. However, transcapacitive sensing methods that use routing traces disposed under the sensor electrodes are susceptible to high background capacitive coupling between the traces and the sensor electrodes utilized to drive the modulated signal utilized for generating the electric field between the sensor electrodes. High background capacitance undesirably decreases the signal to noise ratio, making accurate touch sensing more difficult.
Thus, there is a need for an improved touch sensor device.